The present invention relates to a method of making a multilayer, thin film laminate printed circuit and an electrically fired blasting cap for detonating a secondary explosive made from such a circuit. In more detail, the present invention relates to a method of making a multilayer printed circuit including a thin film laminate of a type which would likely be damaged if the circuit was made by conventional multilayer techniques. That method makes possible the construction of such a circuit for uses such as in a blasting cap.
A number of applications have developed over the past several years for multilayer printed circuit boards, and with those new applications has come increased difficulty in the manufacture of such circuits (see, for instance, R. Fidrych, "Low Pressure Lamination", 10 Printed Circuit Fabrication 46-53 (1987) for a brief summary). One of the design criteria which has contributed to the increased manufacturing difficulty has been the demand for circuits with more layers on thinner innerlayer materials (M. Angelo, "Multilayer Registration Tooling-The Full Spectrum", 10 Printed Circuit Fabrication 24-34 (1987)). In large part, these difficulties are the result of the fragility of the thin film laminates which have been developed for use in such multilayer printed circuit boards, which are easily wrinkled, bent, and/or torn during processing. These tendencies of the thin film laminates may even cause the majority of the multilayer circuits made during a particular production run to be rejects such that the cost of such circuits is so prohibitively high that few can afford them in quantity.
By the use of the phrase "thin film laminate", it is intended to refer to those materials which are laminates of, for instance, a conductive metal and a suitable plastic resin which are manufactured and used in thin film form. Examples of such materials include composites of copper and polyimide resins. For instance, throughout the present specification, reference is made to a laminate of copper and Kapton .TM., the latter being a DuPont trademark for a proprietary polyimide resin. Such a laminate is available under the brand name Microclad .TM. (Fortin Industries, Inc., Sylmar, Calif.) in thicknesses as small as 0.0005 inches and Etch-A-Flex .TM. (Southwall Technologies, Palo Alto, Calif.). This copper/Kapton laminate, however, is merely illustrative of one type of thin film laminate with which the present invention may be utilized, the examples set out herein being set out for purposes of exemplification and compliance with the Patent Statute, and not by way of limitation.
Multilayer printed circuits, as noted above, have a number of applications. For purposes of exemplification, one such application of a circuit made in accordance with the method of the present invention is described herein, namely as a substitute for the primary explosive, or ignition primer charge, in an electrically fired detonator for a secondary explosive. A secondary explosive, or base charge, such as PETN, TNT, HNS, RDX or NONA is generally detonated by a blasting cap which includes an ignition primer charge such as low density nitromannite, diazodinitrophenol, lead styphnate or lead azide. The latter primary explosive is widely used in electrically fired detonators in the oil field, for instance, for perforating a casing. In that use, lead azide has caused many serious injuries and deaths to the personnel handling the charges as a result of untimely detonation, and it is one of the safer primary explosives. A thin film laminated circuit constructed in accordance with the present invention effectively removes all risk of untimely detonation of the base charge by completely replacing the primary explosive.
It is, therefore, an object of the present invention to provide a method of making a thin film laminate printed circuit board.
Another object of the present invention is to provide a multilayer printed circuit board including a thin film laminate.
Another object of the present invention is to provide a method of making a multilayer circuit board including a thin film laminate which can be etched and registered with a high degree of accuracy using standard multilayer techniques.
Another object of the present invention is to provide a method of making a multilayer circuit board in which a thin film laminate can be etched and registered using conventional multilayer techniques without bending, wrinkling or tearing the thin film.
Yet another object of the present invention is to provide an electrically fired blasting cap, or detonator, which includes a printed circuit board including a thin film laminate.
Another object of the present invention is to provide a blasting cap, or detonator, which significantly reduces the likelihood of injury of the personnel handling the explosives.